Method for plating resin material

ABSTRACT

This invention provides a method for plating a resin material that improves adhesion strength between a resin material and a plated metal layer and reduces the cost incurred by plating. This method comprises a step of treating a resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.

TECHNICAL FIELD

The present invention relates to a method for plating the surface of a resin material that improves plate adhesion.

BACKGROUND ART

Electroless plating has been known as a method for imparting electric conductivity or metallic luster to resin materials. This electroless plating refers to a method of forming a metal coating on the surface of a material via chemical reduction and deposition of a metal ion in a solution. Unlike electroplating that allows electrolytic deposition with the aid of electric power, a metal coating can be formed on an insulator such as a resin. Also, electroplating can be applied to a resin material having a metal coating formed thereon, and applications of such material can be expanded. Accordingly, electroless plating has been extensively adopted as a method for imparting metallic luster or electric conductivity to a resin material that is used in the fields of automobile decorative parts, household electrical goods, and the like.

Electroless plating is employed in a variety of fields, particularly for electrifying through holes or via holes in the field of printed-circuit boards.

Disadvantageously, it is time-consuming to form a plated layer via electroless plating, and adhesion between the plated layer and a resin material is insufficient. In general, accordingly, a resin material is first subjected to chemical etching to roughen the surface and is then subjected to electroless plating.

A method is also known wherein a resin material is subjected to pretreatment with ozone gas and then subjected to electroless plating. An unsaturated bond of a resin material is cleaved by ozone gas, the molecular size thereof is lowered, and molecules with different chemical compositions become present on the surface thereof. Thus, surface smoothness is lost and the surface is roughened. Accordingly, a plated layer formed via electroless plating is firmly attached to the rough surface and thus is not easily separated from the material.

In the aforementioned conventional technique, the surface of the resin material is roughened and plate adhesion is enhanced via a so-called “anchor effect.” In such technique, however, the surface smoothness of the resin material is lowered. This necessitates the thickening of the plated layer in order to obtain a sophisticated metallic luster and disadvantageously increases the number of procedures.

In the method wherein the surface is roughened via etching, use of toxic substances such as chromic acid or sulfuric acid is necessary. This method is also problematic in terms of burdens on the environment resulting from the necessity for waste liquid management or the like.

JP Patent Publication (Kokai) No. 2002-309377 A discloses a method of pretreatment for enhancing plate adhesion when forming a plated layer on the surface of a resin material via electroless plating. This method comprises bringing a resin material having an unsaturated bond into contact with a first solution containing ozone and then bringing the resin material into contact with a second solution containing at least either an anionic or nonionic surfactant and an alkaline compound in order to form a plated layer with excellent adhesion without the need of etching, ozone gas treatment, or roughening of the surface of the resin material. In this method, palladium is used as a catalyst for plating.

SUMMARY OF THE INVENTION

A conventional plating technique that involves a combination of chromic acid treatment and palladium plating is problematic in the following respects: the adhesion strength of a plated layer is as low as approximately 1 kgf/cm; the burden on the environment is considerable due to the use of chromic acid; and palladium, which is expensive and experiences significant price fluctuations, is used. Similarly, a combination of ozone water treatment and palladium plating disclosed in JP Patent Publication (Kokai) No. 2002-309377 A involves the use of expensive palladium.

The present invention is directed to improving adhesion strength between a resin material and a plated metal layer when plating a resin material. Also, the present invention is directed to considerably reducing the cost required for plating.

The present inventors have conducted concentrated studies and have consequently found that the aforementioned objects could be attained by employment of ozone water treatment in combination with the use of a specific metal catalyst. This has led to the completion of the present invention.

More specifically, the first aspect of the present invention concerns a method for plating a resin material comprising a step of treating such resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.

The step of treating resin materials with ozone water is carried out by immersing various types of resin materials in ozone water or spraying ozone water on the surface of such resin materials. In general, ozone water comprises water as a solvent; however, it preferably comprises an organic or inorganic polar solvent. This can further shorten the time necessary for treatment. The step of permitting the resin material to adsorb a metal catalyst is carried out by immersing a resin material in a catalyst bath containing a salt of a metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.

In a conventional technique involving surface roughening with the use of chromic acid or the like, for example, a butadiene rubber portion on the surface of ABS resins is dissolved with chromic acid to form pores with sizes on the micron order, and catalyst particles unevenly adhere to the roughened surface. In contrast, the surface of the resin material is evenly activated without roughening, and catalyst particles evenly adhere to the ozone-water-treated surface in the case of ozone water treatment.

Preferably, the method for plating a resin material according to the present invention further comprises a step of alkaline degreasing of the surface of the resin material between the step of treating the resin material with ozone water and the step of permitting the resin material to adsorb a metal catalyst. By carrying out the step of alkaline degreasing, stains on the surface of the resin material can be removed, wettability can be improved, and metal catalyst adhesion can be enhanced.

An alkaline compound that is used in the step of alkaline degreasing of the present invention is capable of dissolving the surface of the resin material at a molecular level and removing an embrittled layer on the surface of the resin material so as to allow more functional groups to appear. Thus, plate adhesion can be enhanced. An alkaline compound that can dissolve the surface of the resin material at a molecular level and remove the embrittled layer can be employed. Examples thereof include sodium hydroxide, potassium hydroxide, and lithium hydroxide. A treatment solution that is employed in the step of alkaline degreasing preferably comprises at least either an anionic or nonionic surfactant.

In the present invention, the step of chemical plating (electroless plating) is preferably carried out following the step of permitting the resin material to adsorb a metal catalyst. Conditions for chemical plating and metal species to be deposited are not limited, and chemical plating can be carried out in a manner similar to conventional electroless plating. An example of preferable chemical plating is Ni—P chemical plating.

In the present invention, the step of electroplating can be carried out following the step of chemical plating. Via an additional step of electroplating, the thickness of the plated layer can be increased. Thus, metallic luster can be imparted, which can result in a remarkably sophisticated plated layer. Conditions for electroplating and metal species to be deposited are not limited, and electroplating can be carried out in a manner similar to conventional electroless plating. Examples of metal species to be deposited include copper, silver, nickel, gold, tin, and cobalt. An example of preferable electroplating is copper sulfate electroplating.

In the present invention, the step of electroplating can be carried out following the step of permitting the resin material to adsorb a metal catalyst without the step of chemical plating.

The ozone content of ozone water significantly affects activation of the surface of the resin material, and activation effects can be observed at a level of approximately 10 ppm. An ozone content of 50 ppm or higher can result in remarkably enhanced activation effects, and at 100 ppm or higher, the treatment can be carried out within a shorter period of time. Since a low ozone content results in weak effects of activating the surface of the resin material, a higher ozone content is preferable. Preferably, the duration of ozone water treatment is between 2 minutes and 10 minutes. If such duration is less than 2 minutes, activation of the surface of the resin material may be insufficient. In contrast, a duration exceeding 10 minutes may cause deterioration in the resin material.

The surface of the resin material is permitted to adsorb a metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts. Among these catalysts, a silver catalyst is preferable in terms of cost and the peel strength of the resulting plated layer.

The method for plating a resin material according to the present invention can be applied to a wide variety of fields. Specifically, the second aspect of the present invention concerns automobile parts, electrical parts, and printed circuit boards plated by the aforementioned method according to the present invention. More particularly, the method for plating a resin material according to the present invention is effective for producing printed circuit boards. Adoption of the method of the present invention for plating the through holes or via holes of the printed circuit boards eliminates the need for the step of surface roughening. Thus, printed circuit boards of higher density can be obtained. Since this method does not involve the use of palladium, which is expensive and experiences significant price fluctuations, the cost can be reduced. Further, the foundation layer of a silver printed circuit board is prepared via chemical plating with the adoption of ozone water treatment in combination with the use of a silver catalyst according to the present invention. Thus, a strong silver printed circuit board comprising a foundation layer integrated with a wiring layer with the aid of a silver component can be obtained.

Adoption of ozone water treatment in combination with the use of a specific metal catalyst for plating a resin material improves the adhesion strength between a resin material and a plated metal layer and significantly reduces the cost incurred by plating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing the procedures carried out in the examples.

FIGS. 2A and 2B show charts showing the results of comparing the adhesion strengths of plated resins prepared in Examples 1 and 2 and Comparative Examples 1 to 4.

PREFERRED EMBODIMENTS OF THE INVENTION

Examples of resin materials that can be used in the present invention include: thermoplastic resins, such as acrylonitrile-butadiene-styrene (ABS) copolymer, acrylonitrile-styrene (AS) copolymer, polystyrene (PS), ethylene-vinyl acetate (EVA) copolymer, polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyacrylonitrile (PA), polyoxymethylene (POM), polycarbonate (PC), polypropylene (PP), polyethylene (PE), a polymer alloy composed of an elastomer and PP, denatured PPO, polytetrafluoroethylene (PTFE), and ethylene-tetrafluoroethylene copolymer (ETFE); and thermosetting resins, such as phenolic resins and epoxy resins. The forms of such resins are not particularly limited.

Ozone water, particularly highly concentrated ozone water, which is employed in the present invention, can be generated in accordance with a conventional technique. For example, highly concentrated ozone water can be generated with the use of an apparatus for generating ozone water that comprises an absorption column. Such apparatus comprises a water inlet and an exhaust gas outlet located at the upper site of a gas absorber and an inlet for ozone-containing gas and an outlet for ozone water located at the lower site of the gas absorber. Aggregates of a continuous gas stream of the gas absorber are generated via fractionation or bending of the gas path, and water is brought into countercurrent contact with ozone-containing gas. Thus, highly concentrated ozone water can be generated.

In general, ozone water comprises water as a solvent; however, it preferably comprises an organic or inorganic polar solvent. Examples of organic polar solvents include: alcohols, such as methanol, ethanol, and isopropyl alcohol; organic acids, such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, hexamethylphosphoramide, formic acid, and acetic acid; and mixtures thereof with water or an alcohol solvent. Examples of inorganic polar solvents include inorganic acids, such as nitric acid, hydrochloric acid, and hydrofluoric acid.

A treatment solution that is employed in the step of alkaline degreasing preferably comprises at least either an anionic or nonionic surfactant. A surfactant having a hydrophobic group that easily adsorbs to the C═O or C—OH functional group is used. The intended effect may not be sufficiently produced with the use of a cationic surfactant and a neutral surfactant; for example, a plated layer may not be formed. Examples of anionic surfactants include sodium lauryl sulfate, potassium lauryl sulfate, sodium stearyl sulfate, and potassium stearyl sulfate. Examples of nonionic surfactants include polyoxyethylene dodecyl ether and polyethylene glycol dodecyl ether.

A solvent of an alkaline degreasing solution containing a surfactant and an alkaline compound is preferably a polar solvent. A representative example of such solvent is water. An alcohol solvent or a water-alcohol mixed solvent may be used according to need. An alkaline degreasing solution can be brought into contact with a resin material after ozone water treatment by, for example, a method wherein a resin material is immersed in such alkaline degreasing solution, a method wherein such alkaline degreasing solution is applied to the surface of the resin material, or a method wherein such alkaline degreasing solution is sprayed on the surface of the resin material.

The surfactant concentration in an alkaline degreasing solution is preferably between 0.01 g/l and 10 g/l. If the surfactant concentration is lower than 0.01 g/l, plate adhesion is deteriorated. If the concentration is higher than 10 g/l, excess surfactant is assembled and it remains as an impurity on the surface of the resin material. This also deteriorates plate adhesion. In such a case, the resin material may be rinsed after the pretreatment to remove excess surfactant.

The concentration of an alkaline compound in an alkaline degreasing solution is preferably a pH of 12 or higher. The effects can be attained even when the pH is lower than 12. In such a case, however, achieving plating to a desired thickness would be very time consuming due to the insufficient number of functional groups that appear on the surface of the resin material.

The contact time between an alkaline degreasing solution and a resin material is not particularly limited, and it is preferably for 1 minute or longer at room temperature. If the contact time is too short, the amount of surfactant that adsorbs a functional group may be insufficient, and plate adhesion may be deteriorated. If the contact time is too long, electroless plating may be sometimes difficult since the layer on which at least either of the C═O or C—OH functional groups has appeared is also dissolved. A contact time of approximately 1 to 5 minutes is sufficient. A higher temperature is preferable. The higher the temperature, the shorter the contact time. A preferable temperature range is approximately between room temperature and 60° C.

The step of alkali treatment may be carried out with the use of an aqueous solution consisting of an alkaline compound, followed by adsorption of a surfactant. Since an embrittled layer may be formed again by the time a surfactant is adsorbed, this step is preferably carried out with the use of an alkaline degreasing solution containing at least either an anionic or nonionic surfactant and an alkaline compound.

It is preferable to carry out the step of alkali treatment following the step of ozone water treatment. According to need, these two steps can be carried out simultaneously. In such a case, a mixed solution of ozone water and an alkaline degreasing solution is prepared, and a resin material is immersed in the resulting mixed solution.

Alternatively, a step for removing an alkaline compound via rinsing may be carried out after the step of alkali treatment. A surfactant is firmly adsorbed to a functional group, and thus, it is known that a surfactant is not removed via rinsing and it remains adsorbed. Accordingly, the effects of a resin material that has been pretreated by the method according to the present invention will not be lost even when a long period of time has passed before the step of chemical plating.

EXAMPLES

FIG. 1 is a flow chart showing the procedures carried out in the examples. Hereafter, the procedures of the examples are described in accordance with the flow chart.

Example 1

An ABS resin substrate was treated with ozone water of 50 to 100 ppm for 2 to 10 minutes (step 01). The substrate was then subjected to alkaline degreasing in a 50 g/l aqueous solution of NaOH at 60° C. for 13 minutes (step 02). If the resin substrate is sufficiently clean, this step of alkaline degreasing can be omitted. Subsequently, the substrate was subjected to a catalytic bath of Ag in a 0.5 g/l aqueous solution of an Ag catalyst at 30° C. for 30 minutes (step 03). The substrate was then subjected to chemical plating with copper in a plating solution containing 3 g/l of copper sulfate, 2 g/l of formalin, and 2 g/l of NaOH at 30° C. for 10 minutes (step 04). Further, the substrate was subjected to electroplating of 2.0 A/dm² in a plating solution containing 200 g/l of copper sulfate, 50 g/l of sulfuric acid, 0.125 g/l of hydrochloric acid, and additives at 30° C. for 30 minutes (step 05). A copper-plated layer with a thickness of 100 μm was deposited on the ABS resin substrate via these procedures.

Comparative Example 1

Copper plating was carried out in the same manner as in Example 1. However, chromic acid treatment was carried out instead of ozone water treatment, and a palladium catalyst was used instead of a silver catalyst.

Comparative Example 2

Copper plating was carried out in the same manner as in Example 1, except that chromic acid treatment was carried out instead of ozone water treatment.

Example 2

Copper plating was carried out in the same manner as in Example 1, except that an epoxy resin substrate was used instead of an ABS resin substrate.

Comparative Example 3

Copper plating was carried out in the same manner as in Example 2. However, permanganic acid treatment was carried out instead of ozone water treatment, and a palladium catalyst was used instead of a silver catalyst.

Comparative Example 4

Copper plating was carried out in the same manner as in Example 2, except that permanganic acid treatment was carried out instead of ozone water treatment.

Plated layers on the plated resins prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were incised at intervals of 1 cm to inspect the adhesion strength using a tensile strength tester. The results are shown in FIGS. 2A and 2B. As is apparent from the results shown in FIGS. 2A and 2B, plated layers with higher density can be formed via the process of plating a resin material according to the present invention in comparison with conventional techniques that involve chromic acid treatment or permanganic acid treatment. This can be realized since the process according to the present invention imposes a low burden on the environment, and employs highly concentrated ozone water and a silver catalyst. An adhesion strength of 1 kgf/cm or higher is sufficient, and it is improved to approximately 1.5 kgf/cm in the examples of the present invention.

INDUSTRIAL APPLICABILITY

The present invention provides a method for plating a resin material that improves the adhesion strength between a resin material and a plated metal layer. Such method can significantly reduce the cost incurred by plating. Such plating is applied particularly to automobile parts, electrical parts, and printed circuit boards, and it imparts strong metallic luster and excellent conductivity thereto. Accordingly, the method for plating a resin material according to the present invention contributes to the production of the aforementioned articles with higher density, allowing widespread use thereof. 

1. A method for plating a resin material comprising a step of treating a resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.
 2. The method according to claim 1, which further comprises a step of alkaline degreasing of the surface of the resin material between the step of treating a resin material with ozone water and the step of permitting the resin material to adsorb a metal catalyst.
 3. The method according to claim 1, which further comprises a step of chemical plating following the step of permitting the resin material to adsorb a metal catalyst.
 4. The method according to claim 3, which comprises a step of electroplating following the step of chemical plating.
 5. The method according to claim 1, which comprises a step of electroplating following the step of permitting the resin material to adsorb a metal catalyst without the step of chemical plating.
 6. The method according to claim 1, wherein the ozone content in the ozone water is 50 ppm or higher.
 7. The method according to claim 1, wherein the duration of ozone water treatment is between 2 minutes and 10 minutes.
 8. The method according to claim 1, wherein the metal catalyst is a silver catalyst.
 9. Automobile parts plated by the method for plating a resin material comprising a step of treating a resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.
 10. Electric parts plated by the method for plating a resin material comprising a step of treating a resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.
 11. A method for plating printed circuit boards comprising plating the through holes and/or via holes of the printed circuit boards by the method for plating a resin material comprising a step of treating a resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts.
 12. Printed circuit boards plated by the method for plating a resin material comprising a step of treating a resin material with ozone water and a step of permitting the resin material to adsorb at least one metal catalyst selected from the group consisting of silver, cobalt, nickel, ruthenium, cerium, iron, manganese, and rhodium catalysts. 